As temperatures climbed into the 90s across the state, throngs of people without masks crowded a South Boston beach Saturday, ignoring repeated pleas from public health officials that face coverings and keeping away from others are essential in the continuing battle against the coronavirus.

Throngs packed the M Street Beach, mostly young adults lounging on towels or folding chairs. The beach had a party atmosphere with beer being passed around and music playing on speakers. Almost no one wore masks on the beach or while wading knee-deep in the water.

“I see why with everything going on this isn’t the best thing to be doing,’’ said Jack Johnson, 27, of South Boston, as he sat among a dozen friends. “But it’s not as bad as Florida.’’

The scene was similar to those in such states as Florida, where cases spiked due to lax adherence to public health guidance about the COVID-19 pandemic. On Saturday, that state reported more than 10,000 new cases, according to the Florida Department of Public Health.

George Annas, director of the Center for Health Law, Ethics and Human Rights at Boston University’s School of Public Health, said he hopes officials will be able to encourage the public to take steps that benefit everyone without resorting to “over the top’’ enforcement mechanisms like closing beaches altogether.

“Obviously the last thing we want to do is turn into Florida, so the state can’t ignore mass gatherings without face coverings or social distancing,’’ Annas said in an e-mail. “Nonetheless, it is an extremely hot weekend day and at least some people may simply be testing the limits to see how seriously the distancing guidelines are on beaches.’’

That scene suggested that as hot, humid weather forecasted to continue for the next few days, public officials may struggle to persuade people to wear masks and practice social distancing.

In Ronan Park, where Maria Fernandez of Dorchester was doing exercises for her back, the 58-year-old had taken off her mask while she was working out and it hung from her wrist.

“It’s not comfortable,’’ she said, “but if you need to use, you need to use.’’

Saturday’s high temperature in Boston was 91 degrees, said Andrew Loconto, a meteorologist with the National Weather Service in Norton, and while temperatures were expected to fall to 70 degrees Saturday night, the humidity will remain.

Sunday will be a scorcher, with high humidity and temperatures in Greater Boston climbing into the upper 90s, Loconto said, and heat indexes will be between 97 to 102. And Monday will also see high humidity, with temperatures in the low 90s, he said.

A little relief will come Monday night, when a cold front brings showers and thunderstorms through the area, with the humidity dipping and temperatures dropping into the low 80s for Tuesday, he said.

At M Street, of the beach’s few older visitors, Jim Harden, 71, of Medford was reading the final chapters of “The Shining’’ near an ice cream truck parked at the edge of the sand — without a mask.

“This is a full house,’’ he said, gazing over the crowded beach. But he was not worried that other visitors were not wearing masks either.

“I wouldn’t have a mask here no matter what and none of these people would either.’’

Not everyone in South Boston was happy to see the crowds. On Twitter, Jerry Tracy, 52, who lives a few blocks away, called the M Street Beach Saturday “a public health crisis waiting to happen.’’

That behavior is irresponsible, he said, given the warnings about the pandemic and the reports of clusters of new cases from crowded beaches and parties in other states.

“All the things that happen in other parts of the country are going to happen here, and the behavior today on the beach is going to be the cause of it,’’ Tracy said in an interview.

In Boston, other beaches saw smaller crowds, but still spotty adherence to health guidance.

Carson Beach was less crowded, although there were a handful of large groups of 15 or more.

Evan G., 25 of Medford was in one of them.

“We’re all social distancing from strangers,’’ he said, noting that most of the group’s members live together. All had masks on hand, he said, though none was visible. Nearby, another group played beach volleyball with “Wagon Wheel’’ as background music.

The importance of masks and social distancing has been repeatedly emphasized by local political leaders. During the spring, Governor Charlie Baker announced rules for people to remain at least 6 feet apart while in public and to wear a mask in circumstances when that isn’t possible.

On Thursday, Baker reiterated those guidelines, calling masks the “most important and significant way’’ to stop the spread.

Mayor Martin J. Walsh, in remarks to reporters Tuesday, emphasized the need for residents to not drop their guard regarding COVID-19. He spoke a day after Boston entered Phase 3 of the state reopening, which had occurred in most of Massachusetts July 6.

Samuel Scarpino, a Northeastern University epidemiologist, said it was concerning that people were not taking the distancing or mask requirements seriously at some beaches this weekend.

While experts strongly suspect the risk of transmission of the coronavirus is lower outdoors, he said, clusters of cases have emerged from crowded beaches and lakes. There is a very high chance, he said, of someone with COVID-19 showing up at the beach.

“Given the critical need to keep case numbers down, if we’re to have any chance of safely reopening K-12 schools this fall, I think the governor and mayor should be watching physical distancing and mask compliance very carefully,’’ Scarpino said in an e-mail.

Not all coastal areas were as crowded with people not complying with guidelines.

At Castle Island Saturday, groups of people took off their masks but remained separated in scattered patches of shade.

Anita Alves of Boston had arrived at 7 a.m. to reserve a spot for a family cookout celebrating her daughter’s birthday, as they always do.

“There’s plenty of space around,’’ she said as she set the picnic table with a unicorn theme for the 9-year-old.

In Gloucester, Mayor Sefatia Romeo Theken ordered beach parking lots closed to non-residents this weekend to help reduce crowding.

Edward G. Conley, the city’s police chief, said that early reports Saturday suggested people were respecting the restriction. The volume of traffic seemed much less than last weekend, he said, and there had been no reports of any serious incidents as of Saturday afternoon.

At Good Harbor Beach, where people had spread out along the shoreline, Meghan DePietri helped her daughter Emily, 7, put on sunscreen.

“I’m grateful that it’s residents only and we don’t have to wait in traffic,’’ DePietri said.

Saturday was a respite from the pandemic for some, including Gigi Ojly, 34, a nurse at a Boston nursing home, who has been among the medical workers who have spent months on the front lines battling the coronavirus.

Saturday was Ojly’s the first weekend off in four months, she said, and she spent it in some of the city’s parks with her 2-year-old daughter, Amira.

Ojly has typically worked 12-hour days for six or seven days a week, she said. And the workers did all they could to help their patients.

“Losing patients, it’s never easy no matter where you go. But for us at the nursing home, we had patients that were with us for over a decade,’’ she said. “We were their family. And we lost them.’’

Craig F. Walker and John Tlumacki of the Globe staff contributed to this report.lucas.phillips@globe.comjohn.hilliard@globe.com